Calcium transport from source to sink: understanding the mechanism(s) of acquisition, translocation, and accumulation for crop biofortification

Calcium (Ca) is an essential nutrient that plays important role in various growth and developmental processes in plant. Plants absorb Ca through roots and deliver it to shoot through the xylem stream. Both physiological and molecular mechanisms are involved in the uptake and transport of Ca that affect the distribution and accumulation of Ca in plant tissues. Cation-exchange capacities (CEC) of rhizosphere, root, stem, shoot, and transpiration pull are the physiological forces which affect Ca movement. However, Ca transporter proteins viz., Ca2+ ATPases, Ca2+ exchangers and Ca2+ channels are the molecular forces that are actively involved in transporting Ca throughout the plant. The activity of these transporters are regulated by Ca sensor proteins. Plants store most of the Ca in bound form with Ca-binding proteins, phytic acid or oxalic acid. The process of Ca translocation and partitioning to different plant parts has both agronomic and economic importance. Hence, the understanding of Ca transport, distribution and accumulation in plants is necessary that would provide better insights in designing strategies to produce crop with higher bioavailable Ca content in the grains. The present review covers the various aspects of Ca transport and accumulation in plants that could help in dissecting and manipulating the key pathways involved in high grain Ca accumulation and designing strategies for efficient Ca biofortification in cereals crops.